1. Intermitent or not, you need to be sure of the result. Also, Apple will still work on it even if its intermitent.
2. You won't be able to show your results obviously. However, you will be able to clearly explain the steps you took to diagnose your device. Basically, you'll let them know you have tried to work it out before coming to them. Furthermore, it shows that your gave them steps to take should they need to replicate the issue. Genius' (almost 95% of them) will take this and roll with it for a replacement. You showed a strong case for it
That does make sense. I realize they need data in order to address the problem. I have turned on the analytic's reporting in case that can provide information for them. I have also purchased a GPS Diagnostic App that will give me visibility of the raw GPS data the phone is getting. That could prove invaluable in troubleshooting this.
I am really curious if the iPhone has the capability to switch over to the Watch GPS in the event of a failure though. It would really explain the situation and does seem to fit with what I saw yesterday. I normally only ever see my Watch charge level fall off like that when I use the GPS for an extended workout. If the iPhone was leaning on the Watch GPS for some strange reason it would explain not only the charge level issue but also the choppy updating as the data is sent from the Watch to the iPhone (a slow connection).